It is known that various homogeneous catalysts or heterogeneous catalysts which possess either acidic or basic sites catalyze the so-called aldol condensation of aldehydes with aldehydes or ketones to give higher molecular weight olefinic aldehydes or ketones. In this condensation, the carbon atom bearing the oxo group in one (hereinafter the first) of the condensing compounds acts as an electrophile and attacks the carbon atom alpha to the oxo-bearing carbon atom in the other (hereinafter the second) of the condensing compounds, with removal of a hydrogen atom from the alpha carbon atom of the second compound and protonation of the oxo oxygen atom in the first compound. The resulting compound is a beta-hydroxy aldehyde or ketone which, under the conditions normally used for the condensation, may undergo dehydration to give the corresponding alpha,beta-enone. For example, the aldol condensation of acetaldehyde alone gives initially 3-hydroxybutyraldehyde which can readily dehydrate under the reaction conditions to give but-2-enal.
If the aldol condensation is carried out in the presence of hydrogen and of a catalyst capable of catalyzing olefin hydrogenation (and this catalyst may be the same as the catalyst used to catalyze the aldol condensation itself, if this catalyst has a site for olefin hydrogenation), the unsaturated enone originally produced can be hydrogenated to produce the corresponding saturated aldehyde or ketone. For example carrying out the aldol condensation of acetaldehyde in the presence of hydrogen and of a hydrogenation catalyst will cause reduction of the olefinic double bond in but-2-enal to give the corresponding saturated aldehyde, namely butyraldehyde, as the final product.
The aldol condensation is a useful reaction for the production of higher aldehydes and ketones from lower, readily available aldehydes and ketones, and is extensively used for this purpose in the organic chemical industry. Several important chemicals are prepared using the aldol condensation of aldehydes as a key synthetic step. For example, a key step in the production of 2-ethylhexanol, a commodity chemical used as a plasticizer, is the aldol condensation of n-butyraldehyde. Also, crotonaldehyde is prepared industrially by the aldol condensation of acetaldehyde.
However, one difficulty frequently experienced in the use of the aldol condensation is its tendency to produce complex mixtures of products. The only structural requirements on the two condensing compounds are that the first compound possess a carbonyl group and at least one hydrogen atom on the carbon atom alpha to the oxo group, and that the second compound possess a ketone or aldehyde group. Since the product of the condensation, before or after any hydrogenation, is itself an aldehyde or ketone and normally has at least one hydrogen atom on the carbon atom alpha to the oxo group, the condensation product can undergo further condensation to produce additional products. Thus, depending on the catalyst and reaction conditions employed, the initial products of the condensation can react with more of the starting materials or with themselves to form oligomeric species or they can cyclize to form cyclic aliphatic or aromatic products.
In most aldol condensations it is, for economic reasons, desirable to optimize the production of only one of the numerous possible products. Although running the aldol condensation at low conversions will sometimes reduce the formation of by-products, such running at low conversion is often impracticable in commercial operation because of the large reductions in throughput which result in a plant of any specific size. Thus, catalysts which selectively catalyze the formation of selected ones of the numerous possible products greatly improve the commercial use of the aldol condensation.
Because molecular sieves can affect product distribution by shape selectivity, that is they can curtail the formation of products that do not have the proper shape to enter or exit the molecular sieve pores, they offer the opportunity to tailor the product distribution from an aldol condensation to maximize production of the desired products by appropriate choices of the molecular sieve catalyst and/or reaction conditions. Accordingly, several attempts have been made to use molecular sieves as catalysts in aldol condensations.
U.S Pat. No. 4,339,606 issued July 13, 1982 to Huang et al. and assigned to Mobil Oil Corporation describes the use of palladium loaded ZSM-5 zeolite as a catalyst for the self-condensation of acetone under hydrogen at 600 psi. and 180.degree. C. to give 4-methylpentan-2-one.
Golodets, G. I.; Pavlenko, N. V.; Korzhova, L. F.; Vaisberg, K. M.; Churkin, Yu. I., Kinet. Katal., 984, 25, 1015 report the self-condensation of acetone over metal-containing zeolites to give a mixture of products.
Sumitomo Chemical Co. Ltd., German Offenlegungsschrift No. 1936203, published 20, July 1968, and British Pat. No. 1,252,335 published 3 Nov., Showa Denko K. K., Japanese patent application Nos. 72/13017 filed 20 Apr. 1972, application No. 73/27288 filed 21 Aug. 1973, application No. 73/27287 filed 21 Aug. 1973, and application No. 73/26736 filed 15 Aug. 1973 report similar reactions.
U.S. Pat. No. 3,728,408 issued 17 Apr. 1973 to Tobias, U.S. Pat. No. 4,011,278 issued 8 May 1977 to Plank, Rosinski and Kerr, and U.S. Pat. No. 4,306,106 issued 15 Dec. 1981 to Kerr, Plank and Rosinski, all assigned to Mobil Oil Corporation, disclose by way of example the aldol condensation of acetone over aluminosilicate zeolites to give mesityl oxide and mesitylene but the catalyst contains no hydrogenation site. These reactions are also discussed in Chang, C. D.; Lang, W. H.; Smith, R. L., J. Catal, 1979, 56, 169 and Chang, C. D.; Silvestri, A. J., J. Catal, 1977, 47, 249, and are reviewed in Chang, C. D.; Lang, W. H.; Bell, W. K. in "Catalysis of Organic Reactions", Moser, W. R. (Ed.), Marcel Dekker: New York, 1981, pp 73-94.
The following papers:
Kuznetsov, 0. I.; Shauki, M. Kh.; Panchekov, G. M., Khim. Kinet. Katal, 1979, 182; PA0 Guseinov, A. D.; Chasova, T. A.; Kuznetsov, A. I.; Panchenkov, G. M., Neft. Gaz. (Vinogradov, V. N. Ed.), 1974, 146; PA0 Kuznetsov. O. I.; Panchenkov, G. M.; Chasova, T. A.; Guseinov, A. D., Neftepererab. NeftKhim. (Moscow), 1973, 44; PA0 Kuznetsov, A. I.; Panchenkov, G. M.; Guseinov, A. M.; Chasova,T. A., Neftpererab. NeftKhim. (Moscow), 1973, 28; PA0 Isakov, Ya. I.; Minachev, Kh. M.; Usachev, N. Ya., Izv. Akad. Nauk. SSSR, Ser. Khim.r 1972, 1175; PA0 Grigor'ev, A. A.; Guseva, S. I.; Pinkhasik, E. V.; Avrekh, G. L.; Sedlyarov, V. A.; Lunin, A. f., Khim. Prom-st. (Moscow), 1981, 73; and PA0 Guseva, S. I.; Grigor'ev, A. A.; Pinkhasik, E. V.; Avrekh, G. L., Neftpererab. NefteKhim. (Moscow), 1979, 45,
examine the condensation of acetone over traditional zeolites such as A, X, or Y zeolites but these materials show rather poor activity, selectivity and lifetime and no hydrogenation occurs.
Dworezkov et al., "Adsorptive properties of aluminumphosphate molecular sieves", in Che and Bond (eds.), Adsorption and catalysis on oxide surfaces (Studies in Surface Science and Catalysis 21), pp. 163-172, (Elsevier, Amsterdam, 1985), discloses the adsorption of acetone on to the aluminophosphate AlPO.sub.4 -5 and subsequent desorption of mesityl oxide and other materials from the aluminophosphate.
U.S. Pat. No. 4,433,174 issued 21 Feb. 1984 and U.S. Pat. No. 4,447,641 issued 8 May 1984, both to Hagen and both assigned to Standard Oil Company (Indiana) discuss the condensation of aldehydes or esters with formaldehyde to give alpha,beta unsaturated aldehydes or esters, respectively, using borosilicate molecular sieves as catalysts. Again, no hydrogenation takes place in these processes. U.S. Pat. No. 4,374,274 issued 15 Feb. 1983 to Hellen, Halbritter and Gramlich, and assigned to BASF describes the use of a palladium on metal phosphate catalyst to effect the condensation of ketones with formaldehyde under hydrogen to give methyl substituted ketones, but this catalyst is not a molecular sieve based catalyst.
It is also known that the closely related Knoevenagel condensation occurs over molecular sieves; see Taylor, G. A., J. Chem. Soc., Perkin Trans. I., 1981, 3132.
None of the molecular sieve catalysts described above are ideal for use in aldol condensations. Some prior art molecular sieve catalysts fail to achieve high selectivities, while others require undesirable process conditions or starting materials.
It has now been discovered that the use of certain non-zeolitic molecular sieves as catalysts in aldol condensations involving aldehydes offers high selectivities, and that these high selectivities can be maintained at high conversions.